William Mathias (11/11/1934 - 29/07/1992), a Welsh composer, born in Whitland (Wales). He was known as a conductor and pianist, and gave or directed many premières of his own works. In 1972 he founded the North Wales Music Festival at St Asaph Cathedral and remained its artistic director until his death. He was made a Commander of the British Empire (CBE) in the 1985 New Year's Honours.

Following the death of his mother in March 1980, he composed the large choral and orchestral work Lux aeterna (first performed at the Three Choirs Festival in 1982) for soprano, mezzo-soprano, contralto soloists, chorus and orchestra. Length: 56'10''.
It contains:
1. Lux aeterna (13'12)
2. Domine Jesu Christe (9'49)
3. Libera me (32'59)